I have made atmospheric corrections to my Landsat 8-OLI raster using 'ENVI FLAASH' having surface reflectance values scaled between 1-100.

Surface Reflectance Image

In ArcGIS I am using simple expression to compute NDVI using 'Raster Calculator' tool as illustrated below.

Input Bands


However, the results are not respectable. The same results are faced using 'ENVI Band Math' tool. Interestingly, this is not the case with the outcome from 'Spectral Indices' or 'NDVI' tools built within ENVI.

NDVI Computed in ENVI using tools

Why there is great discrepancy in results in all these cases?

1 Answer 1


you should either set the calculation in float Float(("nir"-"red"))/("nir"+"red") or multiply by 100 (100*("nir"-"red"))/("nir"+"red"). Your strange results are due to conversion to integer (the default).


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